1. Field of the Invention
The present invention relates to a liquid level and/or volume measuring system using a strain-gauge load cell and a method of measuring a liquid level and/or volume. More particularly, it relates to a liquid level and/or volume measuring system which detects a weight change of a float according to a change in liquid level of a liquid tank using a strain-gauge load cell and signal-processes an detected signal to measure a liquid level and/or liquid volume in high precision, and further relates to a method of measuring a liquid level and/or volume.
2. Description of the Related Art
It is necessary to accurately measure the underground water level, the remainder, or the amount of leaked or evaporated liquid in a fuel tank or a raw material tank of various plants for control of reminder or for smooth raw material supply to the production line.
Most conventional measuring methods to obtain data for the remaining liquid employ a float, and are divided into the following:
(A). First method is that a float is set on the surface of the liquid, and a variation of the variable resistance is measured from the float moving according to a variation in the liquid level by means of a lever. PA1 (B). Second method is that the tension of lines connected to the float is analyzed to move the rotating body, thus measuring a turning volume. PA1 (C). Third method is that a pressure gauge is put in the liquid to measure a variation of the pressure. PA1 (D). Fourth method is that sound wave or light flux is emitted to the surface of the liquid to measure the time of returning.
According to the A and B methods, a float is provided to an object to be measured, for measuring displacement of a contact or variation of a rotation angle. A minute variation, e.g. a variation less than 0.01 cm cannot be measured because of an error by friction force produced at each support or an error created by measuring a rotation angle, and its measuring apparatus is too complicated to increase the production costs.
In the above C method, a minute measurement is impossible by using a variation in the pressure, and a double measurement must be essentially carried out because of an error due to the temperature and atmospheric pressure. In case of measuring water under the ground to the depth of 100 m or more, the measuring apparatus may be damaged by a shock wave due to falling water leaked into tube.
In addition, the D method also creates a lot of errors according to condition of atmospher, temperature, humidity, and shape of the liquid surface.